Another Question

One of the most confusing things to me in this book, is why Estella decides to marry Drummle. On page 363 she says, "Why not tell you the truth? I am going to be married to him." She states earlier that she has no heart, and can never love anyone, so what I don't understand is why she decides to marry someone who is looked down upon in sociey like Drummle instead of someone like Pip.